The present invention relates to a method of manufacturing a valve element adapted to be used in a solenoid valve, such valve element having a disk-shaped leaf spring carrying a movable core fitted thereto.
Control valves for controlling the flow of fluid include flow rate control valves, direction control valves and pressure control valves. The flow rate control valve is designed to modify the flow rate of fluid by providing appropriate resistance to the flow by means of a valve element and the direction control valve is designed to allow or block a flow of fluid in a given direction to shift the direction of a flow of fluid also by means of a valve element, whereas the pressure control valve is adapted to regulate the pressure of the flow of fluid in a fluid circuit by means of a valve element. A solenoid valve is a kind of control valve having a valve element to be operated by means of a solenoid.
Known solenoid valves for controlling the flow rate of fluid flowing through a flow path include the one proposed in Japanese Patent Application Laid-Open No. 7-145873. The proposed solenoid valve comprises a valve housing having two ports and a valve element fitted to the valve housing, the valve element having a valve seal adapted to take an open position for opening a valve seat and allowing the two ports to communicate with each other or take a closed position for closing the valve seat and blocking the communication therebetween.
A solenoid coil is arranged in the valve housing in order to operate the valve element. A fixed core (fixed iron core) and a movable core (movable iron core) are arranged at the center of the coil so that the valve element may be opened and closed by means of the movable core. As valve elements capable of being operated by a movable core, there has been developed a valve element provided with such movable core fitted thereto. The valve element of this type typically comprises a disk-shaped leaf spring, an outer peripheral seal arranged at the outer periphery of the leaf spring, a valve seal arranged on one of the surfaces of the leaf spring in order to open and close the valve seat, and a movable core arranged on the other surface of the leaf spring.
The inventors of the present invention have studied valve bodies having a movable core fitted thereto as well as methods for manufacturing such a valve element. As a result of intensive research efforts, the inventors of the present invention invented a method of placing a leaf spring in a metal mold and molding fluorine rubber into an outer peripheral seal and a valve seal so that a movable core and a leaf spring can be held together by means of the valve seal.
However, the sealing effect of a valve element relative to a valve seat may be ensured when costly fluorine rubber is only used for the valve seal but the arrangement of rigidly holding the movable core in position by means of a fluorine rubber valve seal and preparing the valve seal and the outer peripheral seal simultaneously by molding requires the valve seal to have a large capacity. Then, such a valve seal can be prepared only by using a large volume of costly and heavy fluorine rubber to consequently raise the weight of the valve element and counter all the efforts for reducing the weight of the valve element. Additionally, any attempt for rigidly holding a movable core and a leaf spring together by means of fluorine rubber is accompanied by an insufficient holding strength. Then, the valve element would not be able to enjoy a long service life and the solenoid valve comprising such a valve element would lose reliability.
Therefore, an object of the present invention is to provide a method of manufacturing a highly reliable valve element that can be prepared with a reduced volume of costly fluorine rubber and hence at reduced cost.
Another object of the invention is to provide a method of manufacturing a lightweight valve element.
Still another object of the present invention is to provide a method of manufacturing a highly durable valve element wherein the leaf spring and the movable core are rigidly held together with an enhanced level of strength.
According to one aspect of the invention, the above objects and other objects are achieved by providing a method of manufacturing a valve element adapted to be arranged in a solenoid valve to open and close a valve seat, comprising a step of preparing a leaf spring including an outer peripheral ring section, a hub section having a central hole and one or more than one connection holes and a plurality of radial arm sections for connecting between said outer peripheral ring section and said hub section, a step of forming a ring-shaped outer peripheral seal by vulcanizing and molding an elastic material such as rubber along said outer peripheral ring section, a step of preparing a resin-made valve disk with a central anchoring hole to be fitted to one of the opposite surfaces of said hub section, a step of preparing a movable core having at an end thereof a flange section to be held in contact with the outer surface of said hub section and arranged on said opposite surface of said hub section, a step of preparing a resin-made holder ring to be fitted onto said movable core, a step of forming a valve seal including a main body section to be fitted to the front surface of said valve disk and a holder section to be fitted to the rear surface of said valve disk by vulcanizing and molding an elastic material such as rubber and a step of arranging said valve disk on one of the surfaces of said hub section and said flange section onto the other surface of said hub section to make them contact with each other and ultrasonically welding said valve disk and said holder ring while holding said holder ring in engagement with said movable core and in contact with said valve disk so that said movable core is fitted to said leaf spring by means of said valve disk and said holder ring to be made integral with said valve disk.
Said holder ring may be provided with one or more than one meltable projections held in contact with said valve disk by way of said one or more than one connection holes respectively. Alternatively, said valve disk may be provided with one or more than one meltable projections held in contrast with said holder ring by way of said one or more than one connection holes respectively. Said holder ring is provided with a stepped section into which said flange section is put. Said valve disk and said holder ring are made or resin with an average specific gravity of less than 1.9 and apt to be ultrasonically welded. Said movable core is molded from a thin steel plate.